feat(auth): send a request again when its token lapsed in the queue

A request can wait to be served for longer than the access token it was
sent with lives, and comes back refused for a token that was valid when
it left. Uploads that take minutes make that wait ordinary.

- tell an expired token apart from any other refusal by the code the
  API returns, and retry only that one, once
- prefer a token another process left behind over minting a second: it
  saves a round trip, and a rotating provider would retire one that is
  still in use. Assign it rather than read it, since the setter is what
  rewrites the session header the retry will carry
- settle the token before the request so the one compared afterwards is
  the one that was actually sent
- report an overloaded server when the second attempt is refused too,
  and let API errors out of the upload path with their own type

mdrsclient/api/users.py

@@ -8,7 +8,8 @@ from mdrsclient.api.base import BaseApi
 from mdrsclient.exceptions import UnauthorizedException
 from mdrsclient.models import Token, User
 
-# (connect, read) seconds for the token refresh.
+# (connect, read) seconds for the token refresh. Uploads are served by a separate
+# instance, so this one is not queued behind them and has no reason to be slow.
 TOKEN_REFRESH_TIMEOUT: Final[tuple[float, float]] = (5.0, 30.0)